none_t is no loner constructible from literal 0

This caused problems because:
optional<T> o = 0;
always worked. But often it would create an uninitialized optional.

test/Jamfile.v2

@@ -41,6 +41,7 @@ import testing ;
     [ compile-fail optional_test_ref_fail_init_from_Urefref.cpp ]
     [ compile-fail optional_test_ref_fail_assign_from_Trefref.cpp ]
     [ compile-fail optional_test_ref_fail_assign_from_Urefref.cpp ]
+    [ compile-fail optional_test_fail_convert_from_null.cpp ]
     [ compile-fail optional_test_fail_explicit_convert_in_value_or.cpp ]
     [ compile-fail optional_test_fail_explicit_convert_in_value_or_call.cpp ]
   ;

test/optional_test_common.cpp

@@ -51,6 +51,8 @@ using boost::get_pointer ;
 // via the safe_bool operator.
 #if BOOST_WORKAROUND(BOOST_MSVC, BOOST_TESTED_AT(1300) ) // 1300 == VC++ 7.1
 #define BOOST_OPTIONAL_NO_NULL_COMPARE
+#else
+#define BOOST_OPTIONAL_NO_NULL_COMPARE  // Andrzej: I also disable 0 comparison everywhere
 #endif
 
 #define ARG(T) (static_cast< T const* >(0))

test/optional_test_fail_convert_from_null.cpp

@@ -0,0 +1,25 @@
+// Copyright (C) 2014, Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to the Boost Software
+// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// See http://www.boost.org/lib/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+//
+#include "boost/optional.hpp"
+
+//
+// THIS TEST SHOULD FAIL TO COMPILE
+//
+
+struct NoInitFromNull{};
+
+void test_conversion_from_null()
+{
+  boost::optional<NoInitFromNull> opt = 0;
+}
+
+